Hi
I am working on a Sony TA 777ES and this diode may be the reason the input relays keep disconnecting.
I am guessing it is a 7.1v ? zener- I know it is a zener from the service manual- based on the 7H1 part of the description
any thoughts?
I am working on a Sony TA 777ES and this diode may be the reason the input relays keep disconnecting.
I am guessing it is a 7.1v ? zener- I know it is a zener from the service manual- based on the 7H1 part of the description
any thoughts?
The schematic is multi page and I will try and put together the relevant parts.
It is a head scratcher- I did put a 7.1v zener in, and all works until the measured voltage across the diode rises above 7.2v and then they disconnect.
Basically there is a fancy ALPs switch which selects the input, which each have a relay (5v). Everything works fine and then the input drops (lots of relay clicking) so I have been following the voltage, and so far the only consistent thing I can see is if the voltage across the zener is 7.v or less it is OK, above 7.2v it seems to correlate with the relays disengaging.
Thanks
Peter
(manual pages to follow)
It is a head scratcher- I did put a 7.1v zener in, and all works until the measured voltage across the diode rises above 7.2v and then they disconnect.
Basically there is a fancy ALPs switch which selects the input, which each have a relay (5v). Everything works fine and then the input drops (lots of relay clicking) so I have been following the voltage, and so far the only consistent thing I can see is if the voltage across the zener is 7.v or less it is OK, above 7.2v it seems to correlate with the relays disengaging.
Thanks
Peter
(manual pages to follow)
Here are the 4 sections that relate to the input switching and relay power supply
I can post the rest of the manual if that helps- I have recapped the unit- when it works it sounds great and is a 100v Japanese model
I can post the rest of the manual if that helps- I have recapped the unit- when it works it sounds great and is a 100v Japanese model
Can you post the schematic page with the 7V Zener circled? These are kinda blurry.
If this unit is for 100VAC, are you correcting the AC line somehow?
If this unit is for 100VAC, are you correcting the AC line somehow?
I am running it through a Sencore PR57- works well for 100v units
here is the complete manual- Zener on P9
here is the complete manual- Zener on P9
Can of worms. Are the main amp power supply capacitors at the right DC voltage?
Maybe the Sencore is off.
Maybe the Sencore is off.
Sencore is accurate, will double check main power supply caps and report back
and yes it is a real head scratcher....I am very puzzled with this one
and yes it is a real head scratcher....I am very puzzled with this one
Just a guess, the Zener with the relay coils is intended to keep them from chattering as the voltage rises.
If the main caps have about the right DC voltage, that is ruled out as a cause of the odd behavior.
If the main caps have about the right DC voltage, that is ruled out as a cause of the odd behavior.
Ok, look elsewhere then.
Check the actual DC voltage across one of the relay coils as it chatters.
Check the actual DC voltage across one of the relay coils as it chatters.
When the relay that is connected to the input selected -and thus there is signal playing through the amp- there is 0v
on next chatter I will measure and report
on next chatter I will measure and report
The Zener is used to provide a 7.1 V DC supply for the relay coils. The raw voltage comes straight from the main capacitor bank.
The switch controls the relays (relay coil current flow) directly. Depending on the relay coil specifications (are they 5V relays?), the switch contacts will see some current running through them, so the switch might be failing. Easy to check... just remove the switch and measure the contact resistance for ALL positions. You may want to clean the contacts.
I believe the build-up of the switch' contact resistance is your main issue here.... it is probably bad enough for the current to start varying, causing the relay coil to drop. Open the switch and polish the contacts.
How did the problem manifest initially?
Did you replace the Zener with a substitute? If YES, why?
Does the problem occur only for a particular input selected (like for example the CD in)? If YES, that set of switch contacts is failing.
Notice that the Zener will have to drop a fair amount of voltage, from the raw unregulated DC, to only 7.1V required for the relay coil. Depending on the relay coil impedance, that Zener could run (pretty) hot... are there any signs of discolouration on the PCB due to heat?
I do not like Zener diode regulators... If I have to use them, I load them with a resistor to ensure around 10mA current draw at all times. In your case, you should connect a 720-ohm resistor across the Zener. Or even better, use an adjustable 3-pin TO3 regulator set for 7.1V.
Post a photo or 2.. it is easier for us to help you like that.
Good luck.
The switch controls the relays (relay coil current flow) directly. Depending on the relay coil specifications (are they 5V relays?), the switch contacts will see some current running through them, so the switch might be failing. Easy to check... just remove the switch and measure the contact resistance for ALL positions. You may want to clean the contacts.
I believe the build-up of the switch' contact resistance is your main issue here.... it is probably bad enough for the current to start varying, causing the relay coil to drop. Open the switch and polish the contacts.
How did the problem manifest initially?
Did you replace the Zener with a substitute? If YES, why?
Does the problem occur only for a particular input selected (like for example the CD in)? If YES, that set of switch contacts is failing.
Notice that the Zener will have to drop a fair amount of voltage, from the raw unregulated DC, to only 7.1V required for the relay coil. Depending on the relay coil impedance, that Zener could run (pretty) hot... are there any signs of discolouration on the PCB due to heat?
I do not like Zener diode regulators... If I have to use them, I load them with a resistor to ensure around 10mA current draw at all times. In your case, you should connect a 720-ohm resistor across the Zener. Or even better, use an adjustable 3-pin TO3 regulator set for 7.1V.
Post a photo or 2.. it is easier for us to help you like that.
Good luck.
there is no voltage across the colil
Yes they are 5v relays
The switch is sealed, I did put a tiny hole to put in some deoxit as I did think it could be the switch, this usually fixes these sealed units
Th zener was replaced to see if it was the problem, as readings across the old and new zener range form 6.9v to 7.2v (both approx), and when it hits 7.2v the relays chatter.
The problem occurs on a number of inputs
The zener is running at an OK temperature and there is no heat discoloration
I am beginning to think it could be the switch as well, so will pull and measure and report back
The frustrating thing is that it has just worked for an hour or so and no problem
I do hate intermittent faults
Yes they are 5v relays
The switch is sealed, I did put a tiny hole to put in some deoxit as I did think it could be the switch, this usually fixes these sealed units
Th zener was replaced to see if it was the problem, as readings across the old and new zener range form 6.9v to 7.2v (both approx), and when it hits 7.2v the relays chatter.
The problem occurs on a number of inputs
The zener is running at an OK temperature and there is no heat discoloration
I am beginning to think it could be the switch as well, so will pull and measure and report back
The frustrating thing is that it has just worked for an hour or so and no problem
I do hate intermittent faults
Either the switch, or (less likely) the Zener diode voltage rail regulation variation... place a 720 ohm / 2w resistor or thereabouts across Zener, that will reduce voltage variations.
Might also be worth checking if any of the fusibles are associated with that supply - it's just the right age for that...
@Goldie99 - yes good thought
@Extreme_Boky - I am waiting on another set of mini grabbers today for some further tests, though will measure the switch
@rayma -when I have these mini-grabbers I will be able to see voltage on relay for selected input and the other relays
Thanks to all for your assistance so far
@Extreme_Boky - I am waiting on another set of mini grabbers today for some further tests, though will measure the switch
@rayma -when I have these mini-grabbers I will be able to see voltage on relay for selected input and the other relays
Thanks to all for your assistance so far
two additional observations
Pin 3 of Connector 6 from the tone board to the relay/input board measures 35v (fluctuates around 34.5v). When record out switch is off this drops to 19v
Measuring across the LED on the switch module there is about 2v, except when the input drops, then it is about 1.7v (dropped to 0.8v for a less than a second)
As far as I can tell all the switch functions read OK- that is no additional resistance between the connected points.
and of course it is now behaving....
Pin 3 of Connector 6 from the tone board to the relay/input board measures 35v (fluctuates around 34.5v). When record out switch is off this drops to 19v
Measuring across the LED on the switch module there is about 2v, except when the input drops, then it is about 1.7v (dropped to 0.8v for a less than a second)
As far as I can tell all the switch functions read OK- that is no additional resistance between the connected points.
and of course it is now behaving....